3.1 Where are people at risk of being infected with malaria?

About half of the world population lives in areas where there
is some risk of being
infected with malaria. In
109 countries or territories worldwide, malaria is either
constantly present
(endemic) or not present
anymore but with a risk of coming back. These countries are at
different stages in the process of malaria elimination. The
remaining countries are certified malaria-free or have had no
local infections for over a decade (see
Map).

One fifth of the world population is at high risk of
contracting malaria, living in areas with one or more new
malaria cases per 1000 inhabitants per year. Nearly 50% of all
persons at risk of malaria
infection live in the
WHO African Region and 37%
in the
WHO South-East Asia Region.

The vast majority of people at low risk of malaria
infection live outside
Africa in areas with one or more new malaria cases per 1000
inhabitants per year. Although low risk areas cover one third of
the world population living across a huge area, they account for
less than 3% of all reported malaria cases.

3.2 How many malaria cases and deaths were there in 2006?

The numbers of malaria cases and deaths are difficult to
determine with accuracy. In 2006, there were an estimated 247
million malaria cases but the real value could be lower than 200
million or over 300 million. That year, an estimated 881 000
people died from malaria (see
Table of estimates by region).

In 2006 the vast majority of cases and deaths occurred in the
WHO African Region (86%
and 90% respectively), followed by the South-East Asia (9% and
4%) and Eastern Mediterranean
WHO Regions (3% and 4%).

In the
WHO African Region, 90% of
the malaria cases occurred in the 19 countries with the largest
populations and over half were in just five countries: Nigeria,
Democratic Republic of the Congo, Ethiopia, Tanzania and Kenya
(see
number of cases
and
number of deaths by country).

Outside the
WHO African Region: ten
countries accounted for 90% of the malaria cases: mainly India,
which accounted for a third of cases, followed by Sudan,
Myanmar, Bangladesh, Indonesia, Papua New Guinea, Pakistan,
Brazil, Somalia and Afghanistan (see
Fig. 3.6
for number of cases and Fig.3.10 for number of deaths).

The majority of the malaria deaths (85%) occurred in children
under five years of age. The proportion is much higher in the
African and Eastern Mediterranean
WHO Regions than in other
regions (see
Table of estimates by region).

According to data and estimates, only one in five malaria
deaths was reported worldwide in 2006.

3.3 Why is there a wide range of estimates?

It is very hard to calculate the number of malaria cases and
deaths accurately.

Estimates are based, in part, on the numbers of cases reported
by national malaria control programmes. Therefore, whether or
not reported cases are a true reflection of the number of
malaria cases in a region depends on three factors:

The quality of reports from routine surveillance
systems.

The proportion of patients that use public health
facilities compared to those that use private health
facilities or who do not seek
treatment at all. For instance, in South-East Asia a large
number of patients use private services, which results in
official statistics that often report too few new malaria
cases.

The proportion of cases with a confirmed diagnosis.
For instance, in the
WHO African Region
only a small number of samples from patients are sent for
laboratory analysis, and diagnosis is only based on malaria
symptoms such as fever, headache, vomiting and diarrhoea.
This is likely to result in too many cases being reported
because not everyone with signs that could be attributed to
a malaria infection
really has the disease.

In 2006, the WHO
estimated that 1.2 billion people were at high risk of being
infected with malaria and
a further 2.1 billion were at low risk. These figures are
consistent with those from studies carried out in 2003 and 2005
where similar data and techniques were used. Estimates of the
number of deaths (around 1 million deaths per year) are also
broadly consistent with those obtained in a study in 2004. The
main difference is that the new estimates include fewer deaths
in the WHO Western Paciﬁc Region, mainly because malaria seems
to have declined in Cambodia and Viet Nam.

However, the figures are not consistent with those from
studies carried out in the 1990s and from a publication from
2008. Some of the discrepancies can be due to differences in the
way data are analysed. Others could be due to the way in which
results were analysed or to a true decline in the number of
malaria cases since the 1990s.

With all methods, the calculated values for the number of
cases and deaths are very uncertain. This affects estimates for
each country and the ranking of countries within regions. There
are two methods to calculate the numbers of malaria cases and
deaths: by estimating the likely values from limited data, or by
using routine surveillance data. This latter method is better
but depends critically on the information that each country
gives to the WHO and on
data from published surveys. If information is incomplete but
the number of missing reports is registered, the estimates can
be adjusted properly. However, if these records are not kept,
the adjustments could overestimate or underestimate the number
of malaria cases and deaths. Unfortunately, surveillance systems
and registration is weakest in countries most affected by
malaria and that could lead to very large differences between
calculated and actual values.